New Technique - JVC KD-A77 A Service Manual

New Technique
Combination SA heads for recording and playback (Fig. Al
Due to its high recording density, Metal Tape requires
recording and playback heads that are made of materials
having a greater maximum magnetic flux density than con-
ventional ferrite or permalloy. The combined
record/playback heads, newly developed for the KD-A 77,
both employ SA (Sen-Alloy) to ensure high performance.
The SA head has advantages over conventional heads in
various fields such as fewer core loss, greater gap ac-
curacy, better wear and corrosion resistance. However,
its biggest feature is its high maximum magnetic flux densi-
ty. Because of this, the SA head can bring the most out of
the superior performance of Metal Tape. This is especially
true for its extended frequency response at high frequen-
cies; something that has never been possible to realize with
usual cassette tapes.
The playback head incorporates a unique X-cut core struc-
ture to improve the characteristics of the low frequency
range. With ordinary core configurations, playback output
is subject to peaks and dips in the low frequency range as
shown in Fig. B. This is called the "contour effect". :this
effect is caused by interference between the length of the
tape-to-head contact area and the wavelength of the recor-
ding frequency. With the X-cut design the core is cut
diagonally to enable the tape to leave the head, not abrupt-
ly, but with a gradually lessening contact area.
The result is, as shown in the diagram, reduction of the
contour effect. (Fig.
C)
Configuration of record/playback combination SA heads
CD
SA recording head
®
4/lm gaps
®
1/lm gaps
Fig. A
®
X-cut SA playback head
®
SA chips
®
Shield plate
rJ)
Zinc die-casting head base
- 5 -
KD-A77
A/B/C/E/J/U
Comparison between characteristics of conventional cut
core and X-cut core
c
onventlona
I h d . h
ea
Wit
standard core constructi on
in
~
-.
QJ
>
~
...
:J
B-
:J
0
-11
16
10
@~
I
:J
/
~
/
/,1./
Usign standard curre
/
I
I
I I I
,
nt recorded tape
10 .0 70 100 100 .00
Frequence (Hz)
Fig. B
X -cut core construction
in
:9
a;
>
~
...
:J
Cl.
...
:J
0
11
16
10
t--off----+
Using standard current recorded tape
I I I
10 .0 70 100 100 .00
Frequence (Hz)
Fig. C
Note: SA (Sen-Alloy) is a trademark of JVC.
No.4186